Apparatus for controlling sonic energy distribution

ABSTRACT

A vehicle presence detection system for detecting the presence of vehicles preceding along a roadway. A transmitter produces periodic pulses of sonic frequency. A transducer emits the sonic energy pulses, receives reflected sonic energy from the vehicles and generates electrical signals corresponding to such received energy. A wave guide is interposed at the output of the transducer for setting up substantially a line source of sonic energy providing an operating elliptical pattern of a minimum intensity over the roadway. Detection circuitry is actuated to manifest the distinctive indication of vehicle presence.

G 1 white States Eateiit 11 1 1111 3,760,343 Auer, Jr. 1 Sept. 18, 1973[54] APPARATUS FOR CONTROLLING SONIC 3,396,366 8/1968 Midlock et al.340/1 T ENERGY DISTRIBUTION FOREIGN PATENTS OR APPLICATIONS Inventor: Jh u J Fairport, NY. 821,371 7 1949 Germany 179/1155 [73] Assignee:General Signal Corporation,

Rochester Primary ExaminerBen amln A. Borchelt Assistant Examiner-N.Moskowitz [22] FIIedI I972 Attorneyl-larold S. Wynn et al.

[21] Appl. No.: 242,854

Related us. Application Data I57] ABSTRACT [62] Division of Sen 867 621Oct 20 1969 Pat A vehicle presence detection system for detecting the3,672,462. I I I presence of vehicles preceding along a roadway. Atransmitter produces periodic pulses of sonic fre- 52 us. Cl 340/1 T,18l/.5 NP, 340/38 quency- A transduceremits the Sonic energy Pulses, 511Int. Cl. Gls 9/66 wives reflected Sonic energy from the vehicles and[58] Field of Search 340/8 RT, 8 1., 38, generates electrical Signalscorresponding to Such 340/1 T; 179/115, H; 33 3 95 8'; 31/31 A ceivedenergy. A wave guide is interposed at the output 31 p of the transducerfor setting up substantially a line source of sonic energy providing anoperating elliptical 5 References Cited pattern of a minimum intensityover the roadway. De- UNITED STATES PATENTS tection circuitry isactuated to manifest the distinctive indication of vehicle presence.1,845,768 2/1932 Stokes 181/31 A 3,474,400 10/1969 Auer et al. .6Claims, 14 Drawing Figures TRANSMIT TIME R mi 2212. T l M ER GENERATORGENERATOR TRANSDUCER RESET RELEASE TIMER TIME OUTPUT INDICATOR 1 v lRECEIVER RECEIV EIVER GATE Two P PULSE ULSE DETECTION ISOLATOR AMPLIFIERTIMER ug DETECTOR SET MEMORY RESET l6 l7 23 24 25 \IB PATENTED SEP1 81975 sum 5- or 5 FIG. l2

APPARATUS FOR CONTROLLING SONIC ENERGY DISTRIBUTION This is a division,of application Ser. No. 867,62l filed /20/69, now US. Pat. No.3,672,462.

BACKGROUND OF INVENTION The present invention relates to sonic detectorsystems and more particularly to systems capable of distinquishingvehicle reflected signals in a defined zone.

Sonic detection systems find utilization in a number of applications,for example, traffic control and garage supervision. This inventiondescribes a system primarily intended for the detection and indicationof vehicle presence for traffic control.

In a typical application, detection systems transmit short durationpulses of vibration energy, preferably within the ultrasonic frequencyregion. These pulses are directed toward the vehicles by transducerapparatus which also produces electrical signals by responding toreflected energy from the roadway and vehicle surfaces. The roadwayreflections are gated out of the sys-' tem and have no effect upon itsoperation. Those signals reflected from the vehicle or object arerecognized and produce a distinctive indication of vehicle or objectpresence. Thus, presence of a vehicle or object on the roadway isindicated whenever sufficiently strong reflections of sonic energy arereceived by the transducer apparatus within the vehicle gate interval.

In practice, systems using ultrasonic techniques have provensubstantially successful and adaptable to various environments andtargets. However, due to the nature and design of those presentlydeployed systems, all in varying degrees are limited by certainoperation deficiencies. Primarily these deficiencies may be related tothe inability of the system to adequately distinguish false signals,either generated within the system or present in the environment, fromsignals actually reflected from the surface of the vehicle or objectunder scrutiny. Noise or false signals mainly result from electricalcoupling within the system and ringing or continued vibration of thesonic transducer after transmission of each sonic pulse. The lattersource of noise is the use of a single sonic transducer for bothtransmitting and receiving. Another noteworthy problem concernsvibrations in reflected signal strength due to differences in shapes andsizes and materials of the vehicle or objects. Variation occurs inreflected signals also because the initial pulses are projected in lobesof high and low intensity patterns. That is, over a desired zone ofdetection, the intensity of the pattern of pulses projected by thetransducer varies significantly to cause sensitivity problems. When awide detection zone is desired, apparatus necessary for detection in alarge zone is multiplied because the so-called low intensity areas mustbe covered with at least a minimum intensity pattern before asignificant reflected signal can be'utilized.

SUMMARYOF INVENTION There has been provided an electromechanicaltransducer for projecting sonic energy in a peculiar pattern including ahead mounted at the output of the transducer and a wave guide having atransverse slot therethrough adapted to cooperate with the head fordirecting the propagation of the sonic energy to substantially completesonic coverage within a limited range.

An electromechanical transducer apparatus for producing pulses of sonicenergy and respondingly generating electrical signals relative toreceived sonic energy has been provided. A driver generates the sonicpulses and an improvement for projecting the sonic energy in a peculiarcontrolled pattern is a wave guide interposed at the output of thedriver for'controlling the propagation of the emitted sonic pulses. Thewave guide means sets up substantially a line source of sonic energy.The line source eminates the energy in an operating pattern of at leasta minimum intensity near the point of greatest breadth of the pattern.

There has been provided an improved object detection system wherein atransmitter produces periodic pulses of sonic frequency and peculiartime duration. A transducer converts these pulses into emitted sonicenergy pulses and respondingly generates electrical signals relative toreceived sonic energy including energy reflected from the object. Adetector manifests an indication of object presence when actuated and areceiver is rendered responsive for a selected interval to the signalsfor actuating the detector only when signals having a peculiarcharacteristic correlative to the pulses of sonic energy are receivedduring the selected interval. The improvement provides for projectingthe emitted sonic energy in a peculiar pattern wherein a wave guidemeans interposed at the output of the transducer modifies thepropagation of the emitted sonic energy pulses to control the pattern.The wave guide means sets up substantially a line source of emittedsonic energy for spreading the emitted sonic energy pulses in adirection perpendicular to the line source such that an ellipticalpattern of sonic energy is produced and said line source provides anoperating pattern of at least a minimum intensity over the ellipticalpattern.

It is another object of the invention to provide an improved objectdetection system with a controlled detection zone.

It is yet another object'of the invention to provide a vehicle detectionsystem wherein a transducer prodtices a-peculiar pattern of at least aminimum intensity.

It is still another object of this invention to provide a controlledpattern of sonic energy in a controlled area.

It is another object to provide an enlarged pattern of sonic energydistribution.

It is yet another object of the invention to adapt wave guide techniquesto sonic detector systems for increasing the reliability of suchsystems.

The foregoing objects and features of the present invention are clearlyoutlined and explained in the drawings and detailed description.

DESCRIPTION OF DRAWINGS The drawings contain the following:

' FIG. 1 shows one embodiment of the object detection system of thepresent invention.

FIG. 2 shows another embodiment of the object detection system of thepresent invention using two-pulse recognition.

FIG. 3 shows a pattern of emitted sonic energy of a transducer withoutthe improvement of the present invention.

FIG. 3A shows a projection of the emitted sonic energy of FIG. 3 along3A3A.

FIG. 4 shows a pattern of emitted sonic energy of the transducer of thepresent invention.

FIG. 4A shows a projection of the emitted sonic energy of FIG. 4 alongline 4A4A.

FIG. 5 shows a side section elevation of the transducer of the presentinvention.

FIG. 6 is a top elevation of the transducer of the present invention.

FIG. 7 is a portion of the preferred wave guide means.

FIGS. 8 and 9 are side and bottom elevations of the preferred insert,respectively.

FIG. 10 is a side view of a modified wave guide.

FIG. 11 is a side section elevation of the prior art transducer.

FIG. 12 is a front elevation of the modified wave guide of FIG. 10.

DESCRIPTION OF THE EMBODIMENT FIG. 1 shows a detection systemincorporating pulse recognition and detection in which a time basegenerator 10 containing a free-running oscillator of the multivibratoror other similar type generates pulses of desired repetition rate. Thetime base generator 10 has two outputs alternately producing pulses. Thealternate pulses are used to control areceiver gate generator unit 11and a transmitter pulse character generator 12 respectively.

The pulse character generator 12 produces a pulse having anidentification characteristic different from the noise signals eithergenerated or received by the system. A transmitter 14 is controlled totransmit an electrical signal of substantially a single sonic frequencypossessing the same identification characteristic. The transducerapparatus 15 responds to the transmitter 14 by converting thetransmitter 14 electrical signals into a vibratory output ofsubstantially the same frequency and characteristic. It also responds toreflected or environmental sonic energy by generating electricalsignals. Thus the transducer apparatus 15 respondingly produceselectrical signals corresponding to environmental sonic noise andreflected sonic signals.

The receiver gate generator 11 when keyed by the time base generator 10provides a system gate signal activating the receiver circuitry forperiods of time relative to the anticipated receipt of reflected signalsfrom the targets. The receiver isolator unit 16 conducts the electricalsignals to the receiver amplifier 17 and provides the desired impedancelevels for the transducer apparatus. It is primarily needed inapplications where a single transducer for both transmitting andreceiving is utilized. The receiver amplifier 17 is tuned to the sonicfrequency of the transmitted pulse and thus is primarily responsive toonly those signals containing energy within its band. The gate signalsupplies bias voltage to the first stage of the receiver amplifier l7,and thus controls its response. When no gate signal is present, the gainof the receiver amplifier 17 is essentially zero while during the gatesignal interval it reaches a value determined by the parameters of thecircuit. This gain control prevents the amplifier from responding tosignals received at times other than those anticipated for reflectedtarget signals. Amplifier gain is also modified during the-gate intervalby other circuitry to further control the response of the system toringing signals and variations in signal strength. These controls willbe more fully described in ensuing detailed descriptions.

The recognition detector 18 responds only to those amplifier signalshaving the peculiar identification characteristic of the transmittedpulse. If the received electrical signal is coincident with the gatesignal and has a characteristic correlative to the peculiar character ofthe transmitted pulse, the recognition detector 18 circuitry willrespond. The recognition detector 18 circuitry may be conditioned torespond only to a plurality of reflected signals received within aparticular selected interval ranging over a number of transmissioncycles. Should the requirements of the recognition detector 18 be met,it initiates an alteration in the detection memory 19.

The detection memory 19 when altered to a second stable state, producesa distinctive indication of vehicle presence and also causes a releasetimer 20 to be activated. Should signals be produced by the recognitiondetector 18 at a rate greater than a predetermined minimum, the releasetimer 20 once actuated, is prevented from producing an output signal. Atsuch time, however, as recognition detector 18 signals cease, relativeto the removal of the object or vehicle from the detection zone, therelease timer 20 times out and extinguishes the presence indication inthe detection memory 19, thus conditioning the system for detection ofsucceeding vehicles or object. The detection memory 19 contains afeedback feature represented by line 21 which increases the gain of thereceiver amplifier after detection is accomplished. The increased gainprevents loss of recognition due .to reductions in reflected signalstrengths.

An embodiment using multiple pulse detection is also detailed. It musttherefore be kept in mind that the various forms shown are intended toshow equipment organizations conforming to the'exigencies of practicalapplications and not necessarily providing the maximum securityavailable for any given situation.

FIG. 2 shows a system embodiment, containing both pulse recognition andplural pulse detection, wherein a time base generator 10 comprising anysuitable freerunning oscillator of required pretition rate, createsrepetitive pulses used to key the transmission of sonic energy andreceiver gate signals. The time base generator 10 output is conducted tothe transmit pulse timer 22, which apparatus provides a pulse output ofapproximately 5 millisecond duration to drive transmitter 14. Thetransmitter output, a substantially monotonic energy pulse of fivemillisecond duration, supplies power to the sonic transducer 15. Thesonic transducer 15, through electromechanical conversion, directscompressional wave front signals, commensurate to the frequency of thetransmitter signal, to interceptthe predetermined path of movingvehicles or objects.

The time base generator output 10 determines the repetition rate ofreceiver gate signals by triggering the receiver gate generator 11. Inresponse to each pulse from the time base generator 10; thereceiver'gategenerator 11 produces an output signal of sufficient duration so as toencompass an interval of time commencing shortly after the cessation oftransducer 15 transmission and ending shortly before the time requiredfor acquisition of the sonic energy reflected from the pavement. If thesystem is used where no pavement reflection exists, then a differenttime may be selected. The receiver gate generator 11 output is utilizedby various parts of the system, viz., the receiver amplifier 17, re-

ceiver pulse timer 23 and gate and memory 24 in the recognition ofreflected vehicle signals.

The sonic transducer in addition to being capable of convertingelectrical energy into mechanical motion, is also sensitive to thereceipt of pressure variations. Pressure variations are caused byambient noise conditions present in the environment of the transducerand energy reflections in response to its own transmitted pulses. Thus,as a transmitted sonic pulse is reflected either from the roadway or apassing vehicle, it is sensed by the transducer 15 and results ingeneration of a voltage output. The voltage output is coupled to thereceiving portion of the system through receiver isolator 16 whichallows the receiver portion of the system to sense reflected signalswhile rejecting excessively large signals produced when voltage or poweris supplied to the transducer 15. Also prevented is the loading of thetransmitter 14 during pulse transmission periods and the transducer 15dui'ing energy reflection periods.

Output from the receiver isolator 16 is conducted to the receiveramplifier 17. The amplifier is tuned to the tonal frequency of thetransmitter-transducer combination and is relatively unresponsive to anyreceived signals not primarily containing that single basic frequency;this results in rejection of a certain amount of noise received fromenvironment effects on the transducer itself. The receiver amplifier 17is rendered responsive by the receiver gate generator 11 signal, thusavoiding responding to energy pulses indicative of transmitted ratherthan reflected signals.

The received signals of specified tonal frequency after amplificationare received by the receiver pulse timer 23 which is arranged to producea signal output upon its recognition of pulses having a time duration inexcess of 3 milliseconds. Further, the received pulses of requiredduration must be coincident with the gate signal provided by receivergate generator 1 1. If these two conditions are met, a signal outputlasting for the remaining duration of the gate signal period is producedby the gate and memory unit 24.

The gate and memory unit 24 is only enabled during the gate periodprovided by receiver gate generator 11. Its memory feature is providedby the bistable character of its circuitry; once energized during thegate interval, it can be only deenergized upon cessation of the gatesignal. Thus, the receipt of reflected signals during the gating periodproduce only a single output from the gate and memory unit 24.

The two-pulse detector unit 25 is actuated if more than a single outputsignal is derived from the gate and memory unit 24 during apredetermined span of time. This interval is selected to encompass oneor more energy transmission cycles, a single cycle consisting of thetime between successive transmission of energy from the sonic transducer15 as determined by the time base generator 10. System parameters arechosen to demand two received pulses before producing an output from thetwo-pulse detector 25 to indicate the presence of a passing vehicle orobject of this condition ultimately distates the cycle time of thesystem dependent upon the transducer 15 coverage and the maximum speedof the vehicles.

The two-pulse detector 25 output then effects a change of state in thedetection memory unit 19. Once the detection memory unit 19 is altered,it remains so until output signals from the gate and memory unit 24cease for longer than a certain maximum period. The desired period,before resetting of the detection memory unit 19, is determined byspecified operational requirements and implemented by a release timerunit 20. The release timer unit 20 starts to time out whenever a signalis produced by the detection memory unit 19 and is reset to start uponeach receipt of an output signal from the gate and memory unit 24. Thus,as long as signals are being received from the gate and memory unit 24at a certain minimum rate, the release timer unit 20 is not permitted totime out. At such time as these, signals cease for a period commensuratewith the minimum rate, the release timer 20 goes through its time cycleand produces an output signal which in turn resets or clears thedetection memory unit 19.

In addition to the problems described in the previous discussion,difficulties associated with acoustical patterns set up by thetransducer must be discussed. These problems when solved provide forreliability relative to the detection zone pattern and thus increase theefficiency of the electronic improvements previously discussed.

Referring to FIG. 3 of the drawings, the transducer unit 15 without theimprovement of the present invention and its normal sonic pattern isshown. The curve G at a radius D from transducer 15 represents the gateinterval set up by gate generator 11. This wave pattern is of a uniformintensity along line 26. This intensity represents the minimum signalwhich must be transmitted by the transducer unit 15 in order to receivea reflected signal from an object within the detection zone of anyusable intensity. The pattern of FIG. 3 has a major lobe in the centerand two minor lobes to either side of center. This pattern presentscertain difficulties in vehicle traffic detection. The pavement 27 isdivided into two lanes at center lane marker CL; L and R representingleft and right. It is sometimes desirable to be able to detect vehiclesin both lanes L and R. For this reason, transducer 15 is placed abovethe center CL of the highway as shown. Vehicles coming within thedetection zone of the unit 15 reflect sonic pulses from the surface ofthe vehicle to the unit'lS and a suitable electrical signal is generatedfor controlling the associated apparatus. Certain of the reflectedsignals to the transducer 15 are gated out by the timing of the variouscircuits of the system. Generally all signals below 1 or 2 feet from thepavement 27, represented by curve G, are gated out so that there is nopavement reflection to the transducer 15. However, it can be seen fromthe drawing that the areas 29 and 29. indicate that the minimumintensity sonic energy varies along curve G. With this difference inintensity shown merely by way of example in FIG. 3, it is possible tomiss or lose sight of a vehicle in the detection zone. To alleviate thisproblem, it has sometimes been necessary to use separate transducers andplace one over each of the lanes L and R to be certain of positivedetection. This, when multiplied by as many intersections that areusually controlled by systems of this sort, requires additionalequipment which is quite costly.

FIG. 3A is a projection of the pattern provided by transducer 15 upon aplane parallel to the highway containing line 3-3. The outer circle 30shows the extremity of the system or widest range at points A-A'.Circles 31 and 32. define an annular shaped area 33 (unshaded) producedby the rotation of points 8-H and C-C' by about the center CL of thehighway 27,

wherein a substantially less intense signal is received or available inthe detection zone. A vehicle may be present in area 33 and yet bemissed by the detection system. Line 32, the innermost circle, showsagain a high intensity area possibly the width of one lane of trafficwhich would be used in single lane occupancy detection.

FIG. 4 shows the transducer of the present invention with wave guide 34adapted to the output of the transducer 15. This wave guide 34 modifiesthe sonic pulses emitted from transducer 15 by setting up a line sourceat the output of wave guide 34 and produces a pattern having at least aminimum intensity signal over the detection zone. The curve G similar toFIG, 3 at a radius D from the transducer 15 represents the gate intervalset up bygate generator 11. From this all signals below line G are gatedout by the system and transducer 15 is not responsive to reflectedsignal from any objects beyond curve G. Comparing FIGS. 3 and'4, it isapparent that empty areas 29-29 of FIG. 3 are not present within curve Gand therefore the whole detection zone is filled. g

FIG. 4A is a pattern 30' of the sonic energy in a plane including line4A-4A parallel to the highway. The pattern in FIG. 4A shows anelliptical shape 30' covering more of an area than the pattern in FIG.3A. The curbs 36-36 shown in FIGS. 3A and 4A define the width of thehighway 27. It is clear that the projection 30 in FIG. 3A does notextend as widely as the projection 30 of FIG. 4A. The elliptical patternmay be arranged to either be longitudinal with the direction of thehighway oracross the two lanes L' and R as shown in FIG. 4A.

It has also been found useful to use the arrangementof the presentinvention with sidefire operationwhen across the highway detection isdesired for three lane detection. That is, the transducer 15 is mountedoff to the side of a highway, projecting sonic energy across the highwayrather than down upon it. The same gating techniques are used aspreviously described, but for particular applications, side-fire may bemoreuseful.

Because of the shape of walls 48 and inserts 52, if the device is usedfor side-fire operation, it is possible for water to collect in the waveguide 34. Slot 51 extending through wall '48 provides for adequate waterdrainage under such circumstances. v v

. As will be explained later, the elliptical shape of the pattern is adirect result of the wave guide 34 being in terposed after output of thetransducer 15. A vehicle anywhere within therange of the device acrossthe highway 27 will be detected whether it is in the'left or right lane.

The transducer 15 and certain components shown in FIGS. 5-9 includes aferro-magnetic base 40 in which is mounted magnet 38 and ferro-magnetcircular pole piece 41 and an outer pole piece 46 located about'polepiece 41 leaving an annular air gap 42 for the flux of magnet 38.Non-ferro-magnetic annular member 37 maintains the alignment of the airgap 42 between outer pole. piece 46 and inner pole piece 41 withoutshunting the. field in the air gap 42. The magnet 38 provides magneticflu'x through inner pole piece 41 across the air gap 42 through outerpolepiece 46, base 40 and back to the bottom of magnet 38. Diaphragm 45having anannular shape for mounting over slot42 includes ring 44 whichfits into slot 42 and is capable-of movement therein. The ring 44 has awire coil 39 built therein, wrapped around, circularly, with the innerp'ole piece 41 and the wire coil 39 is attached by leads 43 to terminalpoints 47 for actuation byelectrical energy. The diaphragm 45 is drivenby ring 44 and coil 39 where it interacts with the magnetic field of themagnet 41 and produces emitted sonic energy pulses in response toelectrical signals impressed in leads 43, and

diaphragm 45 drives coil 39 which generates electrical signals fromreflected pulses. An outer wall 48 is mounted on top of the outer member46 and extends downwardly and inwardly from the top about the outer edgeof diaphragm 45. Head 49 is a conoidal wedge having a defined shapemounted in the center of the transducer through a shank hole 50 throughinner pole piece 41, magnet 38 and base 40 by screw 81. Wave guide 34 isformed by two wedge shaped inserts 52 mounted in the walls 48 oftransducer 45 by screws 53. The wedges 52 provide a passage way formingthe wave guide 34 for pulses of sonic energy to be transmitted throughslot 54. v

FIG. 11 shows a cross section of a typical transducer 60 of the priorart which includes a term-magnetic base 61, a magnet 58 mounted in thebase 61, a circular inner pole piece 62 mounted above the magnet 58 andouter pole piece 63 which is mounted to the base 61, forming an annularair gap slot 64 between the inner pole piece 62 and outer pole piece 63.Non-ferromagnetic annular member 57 maintains alignment of air gap 64between outer pole piece 63 and inner pole piece 65 without shunting thefield in the air gap 64. Magnet 58 provides the flux through inner polepiece 62 across air gap 64 through outer pole piece 63 through the base61 to the bottom of magnet=58. A-diaphragm 65 having an annularshape ismounted over the air gap 64. The-diaphragm 65 has a ring 66 attachedthereto with a wire coil'59 built in about the ring 66, circularly ofthe magnet 62 with leads 67 attached to terminals '68. When anelectrical signal is impressed on terminals 68, a current flows throughring 66 and coil 59 and interacts with the field established by magnet62 and a reflected pulse vibrates diaphragm 65 causing pulses ofelectrical energy tobe generated in ring 66 and coil 59 and transmittedto terminals 68. Outer walls 69 are mounted to the base 61 over outerpole piece 63 about diaphragm 65 and bullet 70 is mounted to base 61through shank hole 71 in base 61, magnet 58 and inner pole piece 62.

, The wave guide 34 of transducer 15 shown in FIG. 6 provides a slot 54at the output of the transducer 15. This slot 54 interfers somewhat withthe propagation of the sonic pulses emitted from the transducer at thediaphragm 45. A line source of sonic energy is set up along slot 54 andthe line source produces a uniformly projected pattern of sonic energy.along the slot 54 which projects the energy in the desired pattern.Theintensity' is spread somewhat in a direction perpendicular to thedirection of the slot. ln'thisway, the transducer 15 can be placed abovetwo lanes of traffic as shown in FIG. 4 and the slot can be aligned withthe direction of trat fic flow such that the line source of sonic energyaligned along slot 54' radiates sonic energy tending to spreadperpendicular to. the direction of slot 54 which generally is alignedwith the traffic flowso that the pattern is spread across the lanes asshown .in FIG. 4A..

The wave guide 34 is composed. of two removable wedgeshaped inserts52-52. Screw 53 fastens the wave guide'inserts 52 to wall 48 andallowsfor the removal of wave guide to permit theuse of the transducer 15 as asingle lane occupancy detector.

The use of wave guide 34 also suppresses secondary oscillations whichmay arise by insertion of the wave guide 34 initially. With reference toFIGS. and 12, it is possible to obtain a pattern similar to that shownin FIG. 4 by placing a plate 73 over the output of transducer 60. Plate73 has a slot 74 therein. There would be an air space 75 between thediaphragm 66 of the transducer 60 and the outer wall 69 such that sonicpulses emitted from the diaphragm 65 may bounce against plate 73 andcause ringing which would actuate the system improperly.

Bullet 49 shown in side and bottom elevations in' FIGS. 8 and 9respectively is incorporated in transducer provides for a smooth exitpath for sonic energy. It fills a gap between the diaphragm 45 and slot54 and inserts S252 so that secondary oscillations will not be reflectedback into the transducer 15 while it is transmitting sonic pulses. Theconoidal wedge-like shape of bullet 49 and the width of slot 54determined by experimentation to obtain the most efficient configurationfor the particular frequencies being used in this application. Typicallythe frequencies range in the area of kilohertz.

The present disclosure describes a system combining sonic energy gatingwith a controlled beam of pulses. The gating the timing of the variouspulses as they are transmitted and reflected back as previouslydescribed are to a degree dependent upon an accurate zone of detection.It is possible to get such an accurate zone by using more than onetransducer. However, this requires additional equipement which often isvery expensive.

The present system provides for a controlled detection zone by using onetransducer having a wider area of detection than has heretofore beenadvisable to use. A higher input to the transducer 15 does notnecessarily increase the effectiveness of the system because the wavepatterns are substantially the same whether there are high or lowintensity inputs. The wave guide means 34 is the device which modifiesthe pulse transmission such that a uniform pattern of sonic energy isdistributed over a desired area. In this case, an elliptical patternsuch that two lanes of traffic may be detected at the same time.

The present invention also provides for a convertible feature to beincorporated into the wave guide 34. This convertible feature makes itpossible to adapt the transducers presently being used to double laneoccupancy detection and also provide for transducers of the presentinvention to be used as single lane occupancy detectors withoutsubstantial change in the cost of the overall detector.

That is it would be possible to substitute the conoidal wedge-likebullet 49 for the prior art bullet and mount inserts 52-52 in alignmentwith the bullet 69 to form the wave guide. In addition, the inserts S252may be removed having a pattern adaptable to single lane detectionwithout a substantial effect on the efficiency of the transducer 15 inother respects.

The removability of wave guide 51, i.e., by removal of wedges S252,provides transducers adaptable to systems which are already inoperation. These devices when combined with the gating techniquesdescribed previously increase the efficiency of operation without asacrifice of a substantial amount of expense and time in installation.

The use of the wave guide means of the present invention provides for anenhanced system wherein controlled beam propagation is provided. Theinvention provides a method of adapting present detectors to the moreefficient operation of the present disclosure by the interposition oftwo inserts forming a wave guide at the output section of presentvehicle detectors in use in addition to the wave guide, a new bullet isinserted for providing a smooth exit for sonic pulses. The use of thwave guide 34 in connection with sonic detectors has not heretofore beenused as a method of controlling the sonic beam. While there are methodsof controlling sound patterns into various directions including socalledsound lenses, the cost, size and excess of reflected secondary signalscausing ringing is prohibitive in the applications for which thesedevices are contemplated. Wave guide 34 when used in conjunction with ahighly efficient sonic transducer produces an energy pattern which isquite efficient and adaptable to the uses for which the invention wasdeveloped, without excess production, installation and maintenanceexpenses.

While there has been described what is at present considered to be thepreferred embodiment of the invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein, without departing from the invention, and it is, therefore,aimed in the appending claims to cover all such changes andmodifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. An improved vehicle presence detection system comprising:

transmitter means producing periodic pulses of sonic frequency andpeculiar time duration; transducer means converting said pulses toemitted sonic energy pulses and respondingly generating electricalsignals relative to received sonic energy including energy reflectedfrom said vehicle;

detector means operable when actuated to manifest a distinctiveindication of vehicle presence;

receiver means rendered responsive for a selected interval to saidsignals for actuating said detection means only when signals having apeculiar characteristic correlative to said pulses of sonic energy arereceived during said selective interval, wherein the improvement'forprojecting the emitted sonic energy in a peculiar controlled patterncomprises:

wave guide means interposed at the output of said transducer means formodifying the propagation of sonic pulses, said wave guide means settingup substantially a line source of sonic energy for spreading saidemitted sonic energy in a direction perpendicular to said line sourcesuch that an elliptical pattern of sonic energy is produced and saidline source of sonic energy providingan operating pattern of at least aminimum intensity over said elliptical pattern.

2. The vehicle presence detection system of claim 1 wherein arectangular opening is formed in said wave guide means for setting upsubstantially a line source of sonic energy.

3. The vehicle presence detection system of claim 2 wherein said linesource of sonic energy is set off along said rectangular openingof saidwave guide and the elliptical pattern is widest in a directionperpendicular to said line source of sonic energy.

ate with the head for directing the propagation of the sonic energy tosubstantially complete sonic coverage within a limited range.

6. The vehicle presence detection system of claim 5 wherein said waveguide means includes a cup positioned for covering the output of saidtransducer means, said cup having side walls at acute angles to the axisof the head projecting from the slot inwardly towards the transducer.

1. An improved vehicle presence detection system comprising: transmittermeans producing periodic pulses of sonic frequency and peculiar timeduration; transducer means converting said pulses to emitted sonicenergy pulses and respondingly generating electrical signals relative toreceived sonic energy including energy reflected from said vehicle;detector means operable when actuated to manifest a distinctiveindication of vehicle presence; receiver means rendered responsive for aselected interval to said signals for actuating said detection meansonly when signals having a peculiar characteristic correlative to saidpulses of sonic energy are received during said selective interval,wherein the improvement for projecting the emitted sonic energy in apeculiar controlled pattern comprises: wave guide means interposed atthe output of said transducer means for modifying the propagation ofsonic pulses, said wave guide means setting up substantially a linesource of sonic energy for spreading said emitted sonic energy in adirection perpendicular to said line source such that an ellipticalpattern of sonic energy is produced and said line source of sonic energyproviding an operating pattern of at least a minimum intensity over saidelliptical pattern.
 2. The vehicle presence detection system of claim 1wherein a rectangular opening is formed in said wave guide means forsetting up substantially a line source of sonic energy.
 3. The vehiclepresence detection system of claim 2 wherein said line source of sonicenergy is set off along said rectangular opening of said wave guide andthe elliptical pattern is widest in a direction perpendicular to saidline source of sonic energy.
 4. The vehicle presence detection system ofclaim 1 wherein the emitted sonic energy from said transducer means isprojected in a substantially minimum density pattern of ellipticalshape, said pattern in a plane substantially parallel to the output ofsaid transducer means.
 5. The vehicle presence detection system of claim1 including a head mounted at the output of said transducer means, saidhead having a wedge-like conoidal body having acuate sides, and saidwave guide means having a transfer slot therethrough adapted tocooperate witH the head for directing the propagation of the sonicenergy to substantially complete sonic coverage within a limited range.6. The vehicle presence detection system of claim 5 wherein said waveguide means includes a cup positioned for covering the output of saidtransducer means, said cup having side walls at acute angles to the axisof the head projecting from the slot inwardly towards the transducer.